Cuckoo learning When it comes to learning how to identify and mob invading cuckoos, fairy-wrens don't have to go through the school of hard knocks, say researchers. They can simply watch, and learn from their friends.

"This is the first time we've seen any host of a cuckoo go through a social learning process to learn what a cuckoo is," says Feeney, a behavioural ecologist.

"Rather than learning from experience, you can just learn from your friends."

Cuckoos are well known brood parasites, which means they parasitise the parental care of a host bird.

"Brood parasites like cuckoos will never build their own nest and will never raise their own young. They'll just dump an egg in another bird's nest," says Feeney.

One bird that has to contend with becoming a surrogate parent for cuckoos is the superb fairy-wren (Malurus cyaneus).

The cuckoo replaces one of the fairy-wren's eggs with its own while the host is away from the nest. The cuckoo egg looks like a fairy-wren's egg, so the host is none the wiser when it returns.

Then when the hatchling cuckoo emerges from its egg, it turfs its competition out of the nest.

"Within the next few hours it will start getting fairy-wren eggs or chicks on its back and heaving them out of the nest so it's the only one left in the nest," says Feeney.

The cuckoo hatchling also looks and sounds like a fairy-wren chick, so the deception continues, often fooling the surrogate parent right up until the young cuckoo leaves home.

Mob learning

Fairy-wrens can learn to avoid being taken for a 'cuckoo ride' and by identifying them and sounding the alarm to trigger others to gang up on the imposter.

And if all else fails, the host can abandon the cuckoo-invaded nest and start a new one so it doesn't waste its energy bringing up a cuckoo.

But how does a fairy-wren learn about cuckoos in the first place?

"Usually you learn about something through experience, but because the cuckoo is so secretive about what it does fairy wrens don't often get a chance to learn," says Feeney.

One hypothesis is that the fairy-wrens learn by watching others.

"By learning from their friends, they can really speed up the process of learning how to identify and fend off the enemy."

Feeney and colleagues tested this idea by studying the behaviour of fairy-wrens in the Australian capital of Canberra.

Naive birds

Using several groups of fairy-wrens they identified those birds in the group that hatched at the end of summer after the cuckoos had left for their annual pilgrimage around Australia, Indonesia and Papua New Guinea.

They then tested what happened when these naive wrens, that had never seen a cuckoo, were shown a stuffed cuckoo in a cage near their nest.

"They didn't react at all. One even hopped up to the cage to have a look at it," says Feeney.

They then showed the entire group of birds the stuffed cuckoo and got a very different response.

"The experienced birds would make all sorts of alarm calls and try and attack the stuffed cuckoo in the cage," says Feeney.

Finally, they showed the cuckoo to the naive wrens that had just witnessed their friends mobbing the enemy.

"We found that after they had an opportunity to watch their group members mob the cuckoo, they put out alarm calls to help bring in other birds to help mob it," says Feeney.

"This tells us that fairy-wrens can learn what a cuckoo is and how to react to it just by watching their group members mob it rather than by experiencing brood parasitism themselves."